1. Field of the Invention
This invention relates to a photoreceptor for electrophotography, particularly to complexes of charge generating materials useful in forming electrophotographic media, particularly complexes of organic charge generating materials with a) charge transfer materials or b) electron transfer materials and preferably complexes of a new crystalline form of titanium phthalocyanine. The photoconductor systems are suitably used for any electrographic or electrophotographic process such as those used in printers, copying machines, etc. The photoconductor systems may have high sensitivity to long wavelength light and semiconductor laser beam rather than only to visible light.
2. Background of the Art
Electrophotographic photoreceptors having photosensitivity to visible light have been widely used for copying machines, printers, etc. The materials originally used as electrophotographic photoreceptors, usually inorganic photoreceptors, comprised a photosensitive layer (on a conductive support) comprising selenium, zinc oxide, cadmium sulfide, and other inorganic photoconductive substances as the main ingredients have been widely used. However, these inorganic photoreceptors were not always satisfactory with respect to photosensitivity, thermal stability, water/humidity stability, durability and other characteristics required in electrophotographic photoreceptors for copying machines and others. For instance, selenium is inclined to be crystallized by heat or stained by fingerprints, which easily deteriorate the desired characteristics of the photoconductor. Electrophotographic photoreceptors using cadmium sulfide are inferior in water stability and durability and those using zinc oxide have a problem in durability, especially with regard to humidity and physical stress. Electrophotographic photoreceptors using selenium and cadmium sulfide also have disadvantageous restrictions in their manufacture and handling.
To improve upon and avoid such problems of inorganic photoconductive substances, various organic photoconductive substances have been used for photosensitive layers of electrophotographic photoreceptors. For instance, an organic photoreceptor using a photosensitive layer containing poly-N-vinyl carbazole and 2,4,7-trinitrofluorenone is disclosed in Japanese Unexamined Patent Publication No. 50-10496. This photoreceptor is, however, not sufficient with respect to sensitivity and durability. Therefore, an electrophotographic photoreceptor of the separated function type with two layers, a photosensitive layer composing a carrier generating layer and a carrier transporting layer independently, which respectively contain a carrier generating substance and carrier transporting substance, were developed. This enables different substances to assume the carrier generating function and carrier transporting function independently. Therefore, a wide range of substances can be selected that have one of the functions.
Thus, it is expected to obtain organic photoreceptors with high sensitivity and durability. Many carrier generating substances effective for the carrier generating layer of electrophotographic photoreceptors of the separate function type have been proposed. As an example of those using inorganic substances, amorphous selenium can be used as presented in the Gazette for the Japanese Unexamined Patent Publication No. 43-16198. This carrier generating layer containing the amorphous selenium is used in combination with a carrier transporting layer containing organic carrier transporting substance. However, the carrier generating layer comprising the amorphous selenium has the trouble of crystallization due to heat resulting in deterioration of the characteristics as described above. As an example using an organic substance as the carrier generating substance, there are organic dyes or pigments. For instances, those with a photosensitive layer containing bis-azo compounds represented in the Gazettes for Japanese Unexamined Patent Publication Nos. 47-37543, 55-22834, 54-79632, 56-116040, etc. have been already known.
However, though these bis-azo compounds represent relatively favorable sensitivity in the short and medium wavelength ranges, they are low in sensitivity in long wavelength range. It was difficult to use them in laser printers which use semiconductor laser beam sources and they require high reliability.
The gallium aluminum arsenide (Ga/Al/As) type light emitting element which is now widely used as semiconductor laser is more than 750 mm in oscillating wavelength. In order to obtain electrophotographic photoreceptors of high sensitivity for such long wave length light, many studies have been done. For instance, such a method was conceived as to add sensitizing agent to photosensitive materials such as Se, CdS and others with high sensitivity in the visible light range to make the wavelength longer. As described above, however, Se and CdS have not yet sufficient environmental resistance to temperature, humidity, etc. Also, a large number of organic type photoconductive materials have been known as described above; their sensitivity is limited to the visible light region below 700 nm usually and only a very small number of materials have enough sensitivity for longer wavelengths.
Among available charge generating materials, phthalocyanine type compounds are known to have photosensitivity in the long wavelength region. Among them, alpha-type titanyl phthalocyanine is presented in the Gazzette for the Japanese Unexamined Patent Publication No. 61-239248. This type titanyl phthalocyanine has peaks in terms of Bragg's 2theta angle when exposed to X-rays generated from a CuK-alpha source (wavelength 1.541 Angstroms) at 7.5, 12.3, 16.3, 25.3, and 28.7 degrees. However, its sensitivity is low and electric potential stability is inferior in repeated use and is susceptible to photographic fog in electrophotographic processes using reversal development. Electrification power is also low and a sufficient image density is hard to obtain.
U.S. Pat. No. 4,898,799 describes a photoreceptor containing a titanyl phthalocyanine with the major peaks of Bragg's 2theta angle to the CuK-alpha characteristic X-ray (wavelength 1.541 Angstroms) at least at 9.5±0.2 degrees, 9.7±0.2 degrees, 11.7±0.2 degrees, 15.0±0.2 degrees, 23.5±0.2 degrees, 24.1±0.2 degrees, and 27.3±0.2 degrees group. The production method of titanyl phthalocyanine was performed, for example, with titanium tetrachloride and phthalodinitrile mixed in alpha-chloronaphthalene solvent. The resulting dichloro titanium phthalocyanine (TiCl.sub.2 Pc) was hydrolyzed to obtain alpha-type titanyl phthalocyanine. This was processed by 2-ethoxyethanol, diglyme, dioxane, tetrahydrofuran, N,N-dimethyl formamide, N-methyl pyrrolidone, pyridine, morpholine, and other solvents which are electron donors.
Most system rely upon incidental association of the charge generating material and electron transfer material or charge transfer material. This can lead to variation in consistency within a single product, within lots of the same product, and between runs of the same product. Inconsistency in imaging is never a desirable characteristic.